Having more cows of a particular breed in your Dairy Farm will increase the chances of a calf of the respective breed being found. The Bull has no influence on the breed of calf produced, so the calf is always the same breed as its mother. The only exceptions to this are for the Referee cows, which both produce a plain calf. When milk is collected from a Dairy Farm, the farmer will be alerted if a calf was found. You cannot keep the calves found from your own Dairy Farms, but each calf will be available for up to 5 neighbors to adopt. Currently, the Ox, Black Yak, and Indian Yak cannot be placed in the Dairy Farm (even though, in the real world, they can interbreed with cattle and produce milk).